Turbomachines with decoupled collectors

ABSTRACT

Turbomachines such as air dynamometers are disclosed that include a radial outflow compressor and gas collector. In some examples, the gas collector is designed as a separate component that is coupled to the machine, such as coupled to a frame. In some examples, the collector and frame are intentionally spaced and coupled at discrete points to minimize the transfer of mechanical and thermal energy therebetween. Aspects of the present disclosure also include turbomachines that include at least one impeller bypass flow path for the direct transfer of air between ambient and a location in the collector downstream of the impeller blades. In some examples, such flowpath(s) may allow for the inflow of external ambient air into the collector.

RELATED APPLICATION DATA

This application is a continuation of U.S. Continuation application Ser.No. 16/946,481, filed on Jun. 24, 2020, which application was acontinuation of PCT/US2019/014381, filed on Jan. 19, 2019, and titled“Turbomachines with Decoupled Collectors”; which application claims thebenefit of priority of U.S. Provisional Patent Application Ser. No.62/619,514, filed Jan. 19, 2018, and titled “Radial Outflow Compressorwith Separate Impeller Housing and High-Energy Gas Collector”, and U.S.Provisional Patent Application Ser. No. 62/634,609, filed Feb. 23, 2018,and titled “Air Dynamometer”, each of which application is incorporatedby reference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to the field of turbomachinery.In particular, the present disclosure is directed to turbomachines withdecoupled collectors.

BACKGROUND

A compressor is a type of turbomachine designed to impart energy to aworking fluid with a rotating impeller. The higher energy fluidtypically flows from the impeller into a collector. In some prior artdesigns, the collector and the impeller are in a common housing. Theworking fluid is then typically directed to a pipe or duct via theoutlet flange of the vessel.

SUMMARY OF THE DISCLOSURE

In one implementation, the present disclosure is directed to aturbomachine that includes a compressor including an impeller having aplurality of blades, the impeller rotatably supported by a frame; and acollector coupled to the frame and fluidly coupled to the impeller tocollect air discharged by the impeller; wherein the collector issupported by the frame independently of the compressor.

In another implementation, the present disclosure is directed to aturbomachine that includes a compressor including an impeller having aplurality of blades, the impeller rotatably supported by a frame; and acollector coupled to the frame and operably coupled to the impeller tocollect air discharged by the impeller; wherein the turbomachineincludes at least one impeller bypass flow path for the direct transferof air between ambient and a location within the collector downstream ofthe impeller blades.

In yet another implementation, the present disclosure is directed to amethod of manufacturing a turbomachine including a collector, a frame,and a compressor having an impeller, the impeller having a plurality ofimpeller blades. The method includes providing mechanical and thermalattenuation between the collector, compressor, and frame byindependently supporting the collector and compressor by the frame, tominimize, during operation, the transfer of mechanical and thermalenergy between the collector and compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the disclosure, the drawings showaspects of one or more embodiments of the disclosure. However, it shouldbe understood that the present disclosure is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a perspective view of an air dynamometer including acompressor and collector independently coupled to and supported by aframe;

FIG. 2 is a cross-sectional perspective view of the air dynamometer ofFIG. 1 ;

FIG. 3 is a perspective view of the air dynamometer of FIGS. 1 and 2 ;

FIG. 4 is a perspective view of the collector of FIG. 3 ;

FIG. 5 is a perspective view of the frame of FIGS. 1 and 2 ;

FIG. 6 is a front cross-sectional view of the air dynamometer of FIG. 1showing moveable shrouds in a fully-closed position;

FIG. 7 is a close-up front cross-sectional view of the air dynamometerof FIG. 1 ;

FIG. 8 is another close-up front cross-sectional view of the airdynamometer of FIG. 1 ;

FIG. 9 is a perspective view of another example of a collector made inaccordance with the present disclosure;

FIG. 10 is a perspective cross-sectional view of the collector of FIG. 9coupled to a frame; and

FIG. 11 is an illustration of a computational fluid dynamics calculationof airflow within the collector of FIG. 1 .

DETAILED DESCRIPTION

Aspects of the present disclosure include turbomachines such as airdynamometers that include a radial outflow compressor and gas collector.In some examples, the gas collector is designed as a separate componentthat is coupled to the machine, such as coupled to a frame. Thecollector and compressor may be independently supported by the frame. Insome examples, the collector and frame are intentionally spaced andcoupled at discrete points to minimize the transfer of mechanical andthermal energy therebetween. Aspects of the present disclosure alsoinclude turbomachines that include at least one flow path for the directtransfer of air between ambient and a location in the collectordownstream of the impeller blades. In some examples, such flow path(s)may promote inflow of external ambient air into the machine.

Turbomachines with a separate collector design can provide a variety ofbenefits. For example, high compressor exit velocities, e.g. supersonic,can cause vibrations in the collector. By providing a separatecollector, the transfer of collector vibrations from the collector tothe rest of the machine, such as impeller shaft bearings, is minimized.Also, high gas temperatures, e.g., greater than 400 degrees F., at theimpeller exit can cause thermal stress in the collector. A separatecollector design allows for easier management of such thermal stressesand the ability to minimize the transfer of such stresses to the rest ofthe machine. Manufacturing costs can also be reduced by designing thecollector as a separate component that is coupled to the machine. Forexample, lower cost materials, such as sheet metal, can be used, andtolerances can be lower. By incorporating a flow path for the directtransfer of air between ambient and a location in the collector, coolambient air can be drawn into the collector, thereby minimizing thermalstresses caused by high temperature gas exiting the compressor. Further,the at least one flow path may be located at an interface between thecollector and the impeller shroud, thereby obviating the need to sealthe interface, thereby reducing manufacturing costs. In some examples,the impeller and collector are designed so that during use, thepressure, e.g., a static pressure, at the impeller exit is belowatmospheric pressure, e.g., in the range of approximately −47379 Pa toapproximately −641 Pa (gauge pressure), thereby facilitating an unsealedinterface and the transfer of cooling ambient air into the collector.

FIG. 1 illustrates an example embodiment of an air dynamometer 100 madein accordance with the present disclosure. Air dynamometer 100 includesa collector 102 and a compressor 103 coupled to a frame 104. Frame 104has a U-shape or yoke-shape configuration including a base 106 and twoopposed vertical supports 108 a, 108 b extending vertically from thebase. In the illustrated example, base 106 has first and second ends110, 112, and vertical supports 108 a, 108 b extend along the entirelength of the base from the first to the second ends. Vertical supports108 a, 108 b are spaced from one another, defining a space 114therebetween, and collector 102 is located in the space, positionedabove base 110 and coupled to frame 104. Collector 102 is constructed asa separate component from frame 104 and, as described below, coupled tothe frame at discrete attachment points. In the illustrated example,collector 102 and frame 104 are constructed from different materials,for example, frame 104 may be constructed from cast iron, which can havethe benefit of providing vibration dampening and collector 102 can beformed from sheet metal. In other examples, collector 102 and frame 104may be formed from the same type of material.

FIG. 2 , is a perspective cross-sectional view of air dynamometer 100.As shown, compressor 103 includes an impeller 202 having an impellershaft 204 that is rotatably coupled to vertical supports 108. Impeller202 also includes a plurality of impeller blades 206 (only one labeledin FIG. 2 ). As shown in FIG. 2 , impeller 202 extends through collector102, with impeller blades 206 located within the collector. As describedmore below in connection with FIG. 6 , compressor also includesadjustable shrouds 610, bearing assemblies 604, and shroud adjustmentassemblies 612.

FIG. 3 is a perspective side view of collector 102 and impeller 202.Collector 102 includes front and rear walls 302, 304, and a curvedbottom wall 306 and also includes opposed side walls 308, 310,collectively defining an interior volume for collecting air dischargedby impeller 202. Collector 102 also includes a flange 312 at an exit 313of the collector for connecting to downstream ducting (not illustrated)and an internal partition wall 314 that partitions the internal volumeof the collector into two volumes. Side walls 308, 310 include annularinlets 316, 402 (see FIG. 4 ). As shown in FIG. 3 , impeller 202 isoffset from a centerline 318 of the collector by an offset distance d1,resulting in impeller blades 206 (see FIG. 2 ) being closer to frontwall 302 than rear wall 304 and spaced a first distance d2 from thefront wall and spaced a second distance, d3, from the rear wall, thefirst distance being less than the second distance. As described below,such an offset design can result in improved aerodynamic performance,including reduced gas velocities at collector exit 313, which can reducenoise and vibration.

FIG. 4 is a perspective view of collector 102 and also illustratesmounting brackets 404 configured to couple the collector to the frame ata plurality of discrete attachment points. In the illustrated example,mounting brackets 404 include first and second base mounting brackets404 a, 404 b for supporting the collector on base 110 of frame 104 andcoupling the collector to the base (see FIG. 1 ). Mounting brackets 404also include front mounting brackets 404 c, 404 d, 404 e that areconfigured to couple the collector to a cross brace 116 of frame 104(see FIG. 1, 5 ) and three rear mounting brackets 404 (only rearmounting bracket 404 f illustrated), for coupling the collector to arear cross brace 502 (see FIG. 5 ) of the frame. A width We of collector102 is less than a length of space 114 between opposed vertical supports108 a, 108 b (see FIG. 1 ), thereby providing a spacing S1, S2 (FIG. 6 )between side walls 308, 310 and the adjacent vertical support. Suchspacing S1, S2, facilitates the decoupling of collector 102 from frame104 to minimize the transfer of mechanical and thermal energytherebetween. Mounting brackets 404 extend between collector 102 toframe 104, providing a relatively small number of attachment pointsbetween the collector and frame, to minimize the transfer of mechanicaland thermal energy. In some examples, one or more of mounting brackets404 may also include vibration-damping resilient members (notillustrated). For example, at least one layer of any type of resilientmaterial known in the art for providing vibration dampening, such as oneor more layers constructed from natural rubber, synthetic rubber, orpolymer foam. Mounting brackets 404 may also be designed to allow forsome movement of the collector to allow for thermal expansion of thecollector. Mounting brackets may be designed as isolation mounts or mayincorporate isolation mounts, e.g., elastomeric, spring, or hydraulicisolation mounts. The separate design can allow for vibrations in thecollector 102 to be sufficiently attenuated such that the remainingcomponents of the system, including impeller shaft bearings 606 (FIG. 6) are not adversely impacted. The arrangement also allows for thermalexpansion of the collector, which may be constructed of sheet metal, andthe brackets 404 can also be designed to provide a heat sink functionfor removing thermal energy from the collector. FIG. 5 is a perspectiveview of frame 104 illustrating the yoke-shape configuration of the framewith vertical supports 108 a, 108 b extending vertically from base 110and front and rear cross braces 116, 502 extending between the verticalsupports.

FIG. 6 is a front cross-sectional view of air dynamometer 100. As shown,compressor 103 includes impeller 202, which in the illustrated exampleis a radial outflow impeller, the impeller including a hub 600 and aplurality of impeller blades 602 (only four blades 602 a, 602 b, 602 c,602 d shown). Compressor 103 also includes bearing assemblies 604 a, 604b, which include bearings 606 a, 606 b disposed in bearing housings 608a, 608 b for rotatably coupling impeller 202 to frame 104. Compressor103 also includes shrouds 610 a, 610 b which are moveable in an axialdirection parallel to a longitudinal axis a1 of impeller shaft 204.Shrouds 610 are moveable for controlling the power or energy consumptionof the dynamometer. Shrouds 610 have a complementary shape to an outershape of impeller blades 602, including an annular outer shape and ac-shaped cross section for sliding over the blades, to thereby controlan amount of air reaching the impeller blades. Dynamometer 100 alsoincludes shroud adjustment assemblies 612 a, 612 b that include motors614 a, 614 b, gearing 615 a, 615 b, and chains 616 a, 616 b for movingthe shrouds 610. As shown in FIG. 6 , collector 102 surrounds impeller202, with impeller blades 602 located within the collector. Impellerblades 602 include two opposed rows of blades located on opposed sidesof hub 600 and partition wall 314 is located between the two rows ofblades, creating partitioned interior volumes 620 a, 620 b thatseparately direct compressed air from the two rows of blades through thepartitioned interior volumes towards impeller exit 313. Thus, collector102 and compressor 103 are independently supported by frame 104, and thecollector is not structurally supported by the compressor. Instead, inthe illustrated example, collector 102 and compressor 103 only directlyinterface mechanically where shrouds 610 are slidably disposed withinannular inlets 316, 402 (FIG. 4 ). Such structural separation betweencollector 102 and compressor 103 helps minimize any transfer ofmechanical or thermal energy from the collector to the compressor.

FIG. 7 is a close-up front cross-sectional view of air dynamometer 100.During operation, ambient air enters through annular inlets 316, 402 inthe general direction illustrated by main gas flow path arrows A. Maingas flow path A is defined in part by bearing housings 608 and hubsurface 702 on a hub side and defined in part by annular inlets 316,402, and shrouds 610 a, 610 b on a shroud side. FIG. 7 illustratesshrouds 610 in a fully inserted position, which prevents air fromreaching impeller blades 602. During operation, impeller shaft 204 isdriven by a driving force, such as a motor (not illustrated), and theamount of energy consumed by impeller 202 can be increased by retractingshrouds 610 from impeller blades 602, thereby increasing the volume ofairflow that enters air dynamometer 100 and that is compressed byimpeller 202.

FIG. 8 is a close-up front cross-sectional view of air dynamometer 100.As shown, in the illustrated example, annular inlet 402 of collector 102is configured and dimensioned to closely fit around an outer surface 802of shroud 610 b forming an interface 804 between the collector andimpeller 202 (annular inlet 316 is similarly configured to fit aroundshroud 610 a to form an interface). In the illustrated example,interface 804 is not sealed (and the interface between annular inlet 316and shroud 610 a on the opposite side of the collector is similarly notsealed), thereby creating an impeller bypass flow path B for the directtransfer of air between ambient and an interior volume 620 b of thecollector at a location in the collector downstream of the impellerblades 602. Flow path B, therefore, allows for bypassing impeller 202and the direct transfer of air between ambient and an internal volumes620 a, 620 b of the collector. In other examples, air dynamometer 100may include one or more seals to prevent the flow of gas acrossinterface 804. Examples of seals may include any type of elastomericseal, or labyrinth seal. In some examples, air dynamometer 100 mayinclude a seal that is configured to prevent airflow across interface804, while substantially preventing or attenuating transfer ofmechanical and/or thermal energy between collector 102 and shrouds 610.As noted above, interface 804 is not a structural interface forsupporting the collector. Instead, in the illustrated example, collector102 is structurally supported by frame 104 and compressor 103effectively floats within the collector, with the compressor alsoindependently supported by the frame.

FIG. 8 illustrates main gas flow path A entering between an inner wall808 of shroud 610 b on the shroud side and bearing housing 608 b and hubsurface 702 b on the hub side. Ambient air is compressed and acceleratedby impeller blades 602 and discharged into interior volume 620 ofcollector. Side wall 310 and an outer surface 810 of annular inlet 402of collector define a shelf that promotes some internal recirculation ofair (as illustrated by arrow R) proximate interface 804. In theillustrated example, impeller 202 and collector 102 have an aerodynamicdesign that results in impeller blades 602 generating a negative staticpressure in the interior volume 620 b of the collector proximate theimpeller blades and interface 804, such that ambient air is drawn intothe collector as indicated by arrow B. Such a negative pressure designand unsealed interface 804 can provide a variety of benefits, includingthe introduction of relatively cool ambient air into the collector,which can reduce the temperature of air inside the collector, reducingthermal stress. Recirculation flow paths R facilitated by the collectorshelf at surface 810 also facilitates the inward flow of ambient airinto the collector across interface 804. In other examples, collector102 may have another bypass flow path in addition to or instead ofbypass flow path B at interface 804 for allowing the inflow of ambientair, for example, one or more openings in one or more walls 302, 304,306, 308, 310 of the collector.

FIGS. 9 and 10 illustrate another example of a collector 902 that issubstantially the same as collector 102 and can be used in place ofcollector 102. As with collector 102, collector 902 is designed as aseparate component from frame 104 and compressor 103 which can provide avariety of benefits, including minimizing the transfer of mechanical andthermal energy, e.g., vibrations and heat transfer, between thecollector and the frame and compressor. Collector 902 includes a tophalf 904 and a bottom half 906 that are coupled together at flanges 908,910. As shown in FIG. 10 , unlike collector 102, which is coupled toframe 104 by mounting brackets 404 (see FIG. 4 ), collector 902 isconfigured to be supported by cross braces 116, 502 of frame 104 bypositioning flanges 908, 910 on top of the cross members and attachingthe flanges to the cross members. Collector 902 is, therefore,positioned on top of a portion of frame 104 and suspended by the frame.As with collector 102, collector 902 is not structurally supported bycompressor 103 and the compressor effectively floats within thecollector, with the compressor also supported by the frame. In someexamples, vibration dampening materials may be added, for example,between flange 910 and cross braces 116 and 502 for further isolatingcollector 902 from frame 104. The connection of flanges 908, 910 tocross braces 116, 502 can also allow for thermal expansion of theflanges relative to the cross braces for example, by incorporatingovalized or slotted openings in the flanges that are larger in onedimension than an outer diameter of bolts used to attach the collectorto the frame. In other examples, collector 902 may include additionalmounting brackets, such as mounting brackets 404 (FIG. 4 ), forattaching the collector to frame 104.

FIG. 11 illustrates a computational fluid dynamics (CFD) calculation ofcollector 102 and impeller blades 602 during operation of airdynamometer 100 illustrating air velocities within the collector. Asshown in FIG. 11 , collector 102 has an asymmetric shape and impeller202 is offset in the collector, with the impeller being closer to frontwall 302 than rear wall 304 (see also FIG. 3 ). Arrow R indicates therotational direction of impeller 202 and the illustrated CFD streamtubes show high velocity air is discharged from the impeller bladestowards front wall 302 and bottom wall 306 and then decelerates as theair flows towards rear wall 304 and exit 313 of the collector. Such anasymmetric collector shape and offset impeller location can result inreduced air velocities at the collector exit 313 as compared to acentrally-located impeller and/or a symmetrically shaped collector(i.e., symmetric about a vertical centerline extending parallel to frontand rear walls 302, 304), which can be beneficial for reducing noise andvibration.

The foregoing has been a detailed description of illustrativeembodiments of the disclosure. It is noted that in the presentspecification and claims appended hereto, conjunctive language such asis used in the phrases “at least one of X, Y and Z” and “one or more ofX, Y, and Z,” unless specifically stated or indicated otherwise, shallbe taken to mean that each item in the conjunctive list can be presentin any number exclusive of every other item in the list or in any numberin combination with any or all other item(s) in the conjunctive list,each of which may also be present in any number. Applying this generalrule, the conjunctive phrases in the foregoing examples in which theconjunctive list consists of X, Y, and Z shall each encompass: one ormore of X; one or more of Y; one or more of Z; one or more of X and oneor more of Y; one or more of Y and one or more of Z; one or more of Xand one or more of Z; and one or more of X, one or more of Y and one ormore of Z.

Various modifications and additions can be made without departing fromthe spirit and scope of this disclosure. Features of each of the variousembodiments described above may be combined with features of otherdescribed embodiments as appropriate in order to provide a multiplicityof feature combinations in associated new embodiments. Furthermore,while the foregoing describes a number of separate embodiments, what hasbeen described herein is merely illustrative of the application of theprinciples of the present disclosure. Additionally, although particularmethods herein may be illustrated and/or described as being performed ina specific order, the ordering is highly variable within ordinary skillto achieve aspects of the present disclosure. Accordingly, thisdescription is meant to be taken only by way of example, and not tootherwise limit the scope of this disclosure.

Exemplary embodiments have been disclosed above and illustrated in theaccompanying drawings. It will be understood by those skilled in the artthat various changes, omissions and additions may be made to that whichis specifically disclosed herein without departing from the spirit andscope of the present disclosure.

What is claimed is:
 1. A turbomachine, comprising: a frame; an impeller having a hub, a plurality of blades and first and second shafts extending from opposed sides of the hub, the impeller rotatably supported by the frame by first and second bearings coupled to the first and second shafts; a collector coupled to the frame and fluidly coupled to the impeller to collect air discharged by the impeller; and first and second shrouds located on opposed sides of the impeller blades, wherein the first and second shrouds are coupled to the frame, operably coupled to the plurality of impeller blades, and moveable in a first direction to control a volume of air transferred from the impeller to the collector; wherein the collector is supported by the frame independently of the impeller to mechanically decouple the collector from the impeller and minimize the transfer of mechanical and thermal energy therebetween.
 2. The turbomachine of claim 1, wherein the collector is attached to the frame at a plurality of discrete attachment points, the turbomachine further comprising vibration-damping resilient material located between the collector and the frame at one or more of the discrete attachment points.
 3. The turbomachine of claim 1, wherein the collector is suspended from the frame.
 4. The turbomachine of claim 1, wherein the frame includes at least one vertical support and at least one horizontal cross member extending from the at least one vertical support, wherein the collector is suspended from the at least one cross member.
 5. The turbomachine of claim 1, wherein the collector includes first and second sidewalls, wherein the impeller extends through the collector with the plurality of impeller blades located within the collector and the first and second shafts extending laterally outward of corresponding ones of the first and second sidewalls of the collector.
 6. The turbomachine of claim 1, wherein the collector includes two sidewalls that define openings, wherein the first and second shrouds are located adjacent and radially inward, with respect to a rotational axis of the impeller, of corresponding ones of the openings.
 7. The turbomachine of claim 6, wherein the collector includes a front wall and a rear extending between the two sidewalls, wherein the impeller is located in an interior of the collector and is offset from a centerline of the collector and positioned closer to the front wall than the rear wall and is designed to direct a working fluid in a downward direction along the front wall and an upward direction along the rear wall towards an exit of the collector.
 8. The turbomachine of claim 1, wherein the collector has an asymmetric shape, and a rotational axis of the impeller is offset from a centerline of the collector.
 9. The turbomachine of claim 1, wherein the frame includes two opposed vertical supports, wherein the collector is located between the two opposed vertical supports and surrounds the impeller blades.
 10. The turbomachine of claim 1, wherein the collector includes at least one impeller bypass flow path that is designed and configured for the direct transfer of air between ambient and a location in the collector downstream of the impeller blades.
 11. The turbomachine of claim 10, wherein the first and second shrouds each have an outer surface, wherein the at least one impeller bypass flow path is defined in part by the outer surfaces of the first and second shrouds.
 12. The turbomachine of claim 10, wherein the turbomachine is designed and configured to generate a negative pressure to thereby draw ambient air into the collector through the at least one impeller bypass flow path.
 13. The turbomachine of claim 1, wherein the turbomachine is an air dynamometer.
 14. The turbomachine of claim 1, wherein the turbomachine is an air compressor.
 15. The turbomachine of claim 1, wherein the first and second shrouds have an annular shape that includes an outer diameter and a first side extending radially inward of the outer diameter, wherein the first side and outer diameter define a recess that has a complementary shape to the impeller blades, wherein the movement of the shrouds in the first direction adjusts and extent to which the plurality of impeller blades are disposed within the recess.
 16. The turbomachine of claim 1, wherein the turbomachine includes first and second annular inlets located on first and second opposed sides of the turbomachine, wherein the first and second shrouds are located adjacent the plurality of impeller blades in corresponding ones of the first and second annular inlets.
 17. A turbomachine, comprising: a frame; an impeller having a plurality of blades and first and second shafts extending from opposed sides of the impeller, the impeller rotatably supported by the frame by first and second bearings coupled to the first and second shafts; a collector coupled to the frame and fluidly coupled to the impeller to collect air discharged by the impeller; and first and second annular inlets located on first and second opposed sides of the turbomachine, wherein the first and second annular inlets are substantially the same size and designed and configured as working fluid passageways for drawing ambient air into the turbomachine; wherein the first and second shafts are located in the first and second annular inlets; wherein the collector is supported by the frame independently of the impeller to mechanically decouple the collector from the impeller and minimize the transfer of mechanical and thermal energy therebetween.
 18. The turbomachine of claim 17, further comprising first and second shrouds coupled to the frame, wherein the first and second shrouds are located adjacent the plurality of impeller blades in corresponding ones of the first and second annular inlets.
 19. The turbomachine of claim 18, wherein the collector includes first and second sidewalls that each include an opening, wherein the first and second shrouds are located adjacent and radially inward, with respect to a rotational axis of the impeller, of corresponding ones of the openings in the first and second sidewalls.
 20. The turbomachine of claim 17, wherein the collector is attached to the frame at a plurality of discrete attachment points, the turbomachine further comprising vibration-damping resilient material located between the collector and the frame at one or more of the discrete attachment points.
 21. The turbomachine of claim 17, wherein the collector includes at least one impeller bypass flow path that is designed and configured for the direct transfer of air between ambient and a location in the collector downstream of the impeller blades.
 22. The turbomachine of claim 21, wherein the turbomachine is designed and configured to generate a negative pressure to thereby draw ambient air into the collector through the at least one impeller bypass flow path.
 23. The turbomachine of claim 17, wherein the turbomachine is an air dynamometer. 